The Primate Aging Set-Aside (PAS) colony was established in 1978 to serve as a source of aged rhesus macaques with extensive known medical histories to be used as an animal model for noninvasive research on the processes of aging. It was recognized that the expense of maintaining aged primates was generally beyond the scope and capacity of individual investigators or institutions, and a nationally supported program was established and is maintained to meet future requirements for research on aging using nonhuman primate models. The primary goals of the PAS Colony are to supply, establish, and maintain a group of aged rhesus macaques that are available for research protocols to study the mechanisms and processes of aging, consistent with the National Institute of Aging program guidelines. Efforts will continue to characterize these aged rhesus macaques through daily monitoring of their well-being and annual physical examinations to include hematology and clinical chemistry screening. Animals will be available to investigators to study aging processes on approved projects.